/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.rsocket.internal.jctools.queues;

import static io.rsocket.internal.jctools.queues.LinkedArrayQueueUtil.length;
import static io.rsocket.internal.jctools.queues.LinkedArrayQueueUtil.modifiedCalcCircularRefElementOffset;
import static io.rsocket.internal.jctools.queues.UnsafeAccess.UNSAFE;
import static io.rsocket.internal.jctools.queues.UnsafeAccess.fieldOffset;
import static io.rsocket.internal.jctools.queues.UnsafeRefArrayAccess.allocateRefArray;
import static io.rsocket.internal.jctools.queues.UnsafeRefArrayAccess.calcCircularRefElementOffset;
import static io.rsocket.internal.jctools.queues.UnsafeRefArrayAccess.calcRefElementOffset;
import static io.rsocket.internal.jctools.queues.UnsafeRefArrayAccess.lvRefElement;
import static io.rsocket.internal.jctools.queues.UnsafeRefArrayAccess.soRefElement;

import io.rsocket.internal.jctools.queues.IndexedQueueSizeUtil.IndexedQueue;
import java.util.AbstractQueue;
import java.util.Iterator;
import java.util.NoSuchElementException;

abstract class BaseMpscLinkedArrayQueuePad1<E> extends AbstractQueue<E> implements IndexedQueue {
  byte b000, b001, b002, b003, b004, b005, b006, b007; //  8b
  byte b010, b011, b012, b013, b014, b015, b016, b017; // 16b
  byte b020, b021, b022, b023, b024, b025, b026, b027; // 24b
  byte b030, b031, b032, b033, b034, b035, b036, b037; // 32b
  byte b040, b041, b042, b043, b044, b045, b046, b047; // 40b
  byte b050, b051, b052, b053, b054, b055, b056, b057; // 48b
  byte b060, b061, b062, b063, b064, b065, b066, b067; // 56b
  byte b070, b071, b072, b073, b074, b075, b076, b077; // 64b
  byte b100, b101, b102, b103, b104, b105, b106, b107; // 72b
  byte b110, b111, b112, b113, b114, b115, b116, b117; // 80b
  byte b120, b121, b122, b123, b124, b125, b126, b127; // 88b
  byte b130, b131, b132, b133, b134, b135, b136, b137; // 96b
  byte b140, b141, b142, b143, b144, b145, b146, b147; // 104b
  byte b150, b151, b152, b153, b154, b155, b156, b157; // 112b
  byte b160, b161, b162, b163, b164, b165, b166, b167; // 120b
  byte b170, b171, b172, b173, b174, b175, b176, b177; // 128b
}

// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueProducerFields<E> extends BaseMpscLinkedArrayQueuePad1<E> {
  private static final long P_INDEX_OFFSET =
      fieldOffset(BaseMpscLinkedArrayQueueProducerFields.class, "producerIndex");

  private volatile long producerIndex;

  @Override
  public final long lvProducerIndex() {
    return producerIndex;
  }

  final void soProducerIndex(long newValue) {
    UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, newValue);
  }

  final boolean casProducerIndex(long expect, long newValue) {
    return UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
  }
}

abstract class BaseMpscLinkedArrayQueuePad2<E> extends BaseMpscLinkedArrayQueueProducerFields<E> {
  byte b000, b001, b002, b003, b004, b005, b006, b007; //  8b
  byte b010, b011, b012, b013, b014, b015, b016, b017; // 16b
  byte b020, b021, b022, b023, b024, b025, b026, b027; // 24b
  byte b030, b031, b032, b033, b034, b035, b036, b037; // 32b
  byte b040, b041, b042, b043, b044, b045, b046, b047; // 40b
  byte b050, b051, b052, b053, b054, b055, b056, b057; // 48b
  byte b060, b061, b062, b063, b064, b065, b066, b067; // 56b
  byte b070, b071, b072, b073, b074, b075, b076, b077; // 64b
  byte b100, b101, b102, b103, b104, b105, b106, b107; // 72b
  byte b110, b111, b112, b113, b114, b115, b116, b117; // 80b
  byte b120, b121, b122, b123, b124, b125, b126, b127; // 88b
  byte b130, b131, b132, b133, b134, b135, b136, b137; // 96b
  byte b140, b141, b142, b143, b144, b145, b146, b147; // 104b
  byte b150, b151, b152, b153, b154, b155, b156, b157; // 112b
  byte b160, b161, b162, b163, b164, b165, b166, b167; // 120b
  byte b170, b171, b172, b173, b174, b175, b176, b177; // 128b
}

// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueConsumerFields<E> extends BaseMpscLinkedArrayQueuePad2<E> {
  private static final long C_INDEX_OFFSET =
      fieldOffset(BaseMpscLinkedArrayQueueConsumerFields.class, "consumerIndex");

  private volatile long consumerIndex;
  protected long consumerMask;
  protected E[] consumerBuffer;

  @Override
  public final long lvConsumerIndex() {
    return consumerIndex;
  }

  final long lpConsumerIndex() {
    return UNSAFE.getLong(this, C_INDEX_OFFSET);
  }

  final void soConsumerIndex(long newValue) {
    UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, newValue);
  }
}

abstract class BaseMpscLinkedArrayQueuePad3<E> extends BaseMpscLinkedArrayQueueConsumerFields<E> {
  byte b000, b001, b002, b003, b004, b005, b006, b007; //  8b
  byte b010, b011, b012, b013, b014, b015, b016, b017; // 16b
  byte b020, b021, b022, b023, b024, b025, b026, b027; // 24b
  byte b030, b031, b032, b033, b034, b035, b036, b037; // 32b
  byte b040, b041, b042, b043, b044, b045, b046, b047; // 40b
  byte b050, b051, b052, b053, b054, b055, b056, b057; // 48b
  byte b060, b061, b062, b063, b064, b065, b066, b067; // 56b
  byte b070, b071, b072, b073, b074, b075, b076, b077; // 64b
  byte b100, b101, b102, b103, b104, b105, b106, b107; // 72b
  byte b110, b111, b112, b113, b114, b115, b116, b117; // 80b
  byte b120, b121, b122, b123, b124, b125, b126, b127; // 88b
  byte b130, b131, b132, b133, b134, b135, b136, b137; // 96b
  byte b140, b141, b142, b143, b144, b145, b146, b147; // 104b
  byte b150, b151, b152, b153, b154, b155, b156, b157; // 112b
  byte b160, b161, b162, b163, b164, b165, b166, b167; // 120b
  byte b170, b171, b172, b173, b174, b175, b176, b177; // 128b
}

// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueColdProducerFields<E>
    extends BaseMpscLinkedArrayQueuePad3<E> {
  private static final long P_LIMIT_OFFSET =
      fieldOffset(BaseMpscLinkedArrayQueueColdProducerFields.class, "producerLimit");

  private volatile long producerLimit;
  protected long producerMask;
  protected E[] producerBuffer;

  final long lvProducerLimit() {
    return producerLimit;
  }

  final boolean casProducerLimit(long expect, long newValue) {
    return UNSAFE.compareAndSwapLong(this, P_LIMIT_OFFSET, expect, newValue);
  }

  final void soProducerLimit(long newValue) {
    UNSAFE.putOrderedLong(this, P_LIMIT_OFFSET, newValue);
  }
}

/**
 * An MPSC array queue which starts at <i>initialCapacity</i> and grows to <i>maxCapacity</i> in
 * linked chunks of the initial size. The queue grows only when the current buffer is full and
 * elements are not copied on resize, instead a link to the new buffer is stored in the old buffer
 * for the consumer to follow.
 */
abstract class BaseMpscLinkedArrayQueue<E> extends BaseMpscLinkedArrayQueueColdProducerFields<E>
    implements MessagePassingQueue<E>, QueueProgressIndicators {
  // No post padding here, subclasses must add
  private static final Object JUMP = new Object();
  private static final Object BUFFER_CONSUMED = new Object();
  private static final int CONTINUE_TO_P_INDEX_CAS = 0;
  private static final int RETRY = 1;
  private static final int QUEUE_FULL = 2;
  private static final int QUEUE_RESIZE = 3;

  /**
   * @param initialCapacity the queue initial capacity. If chunk size is fixed this will be the
   *     chunk size. Must be 2 or more.
   */
  public BaseMpscLinkedArrayQueue(final int initialCapacity) {
    RangeUtil.checkGreaterThanOrEqual(initialCapacity, 2, "initialCapacity");

    int p2capacity = Pow2.roundToPowerOfTwo(initialCapacity);
    // leave lower bit of mask clear
    long mask = (p2capacity - 1) << 1;
    // need extra element to point at next array
    E[] buffer = allocateRefArray(p2capacity + 1);
    producerBuffer = buffer;
    producerMask = mask;
    consumerBuffer = buffer;
    consumerMask = mask;
    soProducerLimit(mask); // we know it's all empty to start with
  }

  @Override
  public int size() {
    // NOTE: because indices are on even numbers we cannot use the size util.

    /*
     * It is possible for a thread to be interrupted or reschedule between the read of the producer and
     * consumer indices, therefore protection is required to ensure size is within valid range. In the
     * event of concurrent polls/offers to this method the size is OVER estimated as we read consumer
     * index BEFORE the producer index.
     */
    long after = lvConsumerIndex();
    long size;
    while (true) {
      final long before = after;
      final long currentProducerIndex = lvProducerIndex();
      after = lvConsumerIndex();
      if (before == after) {
        size = ((currentProducerIndex - after) >> 1);
        break;
      }
    }
    // Long overflow is impossible, so size is always positive. Integer overflow is possible for the
    // unbounded
    // indexed queues.
    if (size > Integer.MAX_VALUE) {
      return Integer.MAX_VALUE;
    } else {
      return (int) size;
    }
  }

  @Override
  public boolean isEmpty() {
    // Order matters!
    // Loading consumer before producer allows for producer increments after consumer index is read.
    // This ensures this method is conservative in it's estimate. Note that as this is an MPMC there
    // is
    // nothing we can do to make this an exact method.
    return (this.lvConsumerIndex() == this.lvProducerIndex());
  }

  @Override
  public String toString() {
    return this.getClass().getName();
  }

  @Override
  public boolean offer(final E e) {
    if (null == e) {
      throw new NullPointerException();
    }

    long mask;
    E[] buffer;
    long pIndex;

    while (true) {
      long producerLimit = lvProducerLimit();
      pIndex = lvProducerIndex();
      // lower bit is indicative of resize, if we see it we spin until it's cleared
      if ((pIndex & 1) == 1) {
        continue;
      }
      // pIndex is even (lower bit is 0) -> actual index is (pIndex >> 1)

      // mask/buffer may get changed by resizing -> only use for array access after successful CAS.
      mask = this.producerMask;
      buffer = this.producerBuffer;
      // a successful CAS ties the ordering, lv(pIndex) - [mask/buffer] -> cas(pIndex)

      // assumption behind this optimization is that queue is almost always empty or near empty
      if (producerLimit <= pIndex) {
        int result = offerSlowPath(mask, pIndex, producerLimit);
        switch (result) {
          case CONTINUE_TO_P_INDEX_CAS:
            break;
          case RETRY:
            continue;
          case QUEUE_FULL:
            return false;
          case QUEUE_RESIZE:
            resize(mask, buffer, pIndex, e, null);
            return true;
        }
      }

      if (casProducerIndex(pIndex, pIndex + 2)) {
        break;
      }
    }
    // INDEX visible before ELEMENT
    final long offset = modifiedCalcCircularRefElementOffset(pIndex, mask);
    soRefElement(buffer, offset, e); // release element e
    return true;
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is correct for single consumer thread use only.
   */
  @SuppressWarnings("unchecked")
  @Override
  public E poll() {
    final E[] buffer = consumerBuffer;
    final long index = lpConsumerIndex();
    final long mask = consumerMask;

    final long offset = modifiedCalcCircularRefElementOffset(index, mask);
    Object e = lvRefElement(buffer, offset);
    if (e == null) {
      if (index != lvProducerIndex()) {
        // poll() == null iff queue is empty, null element is not strong enough indicator, so we
        // must
        // check the producer index. If the queue is indeed not empty we spin until element is
        // visible.
        do {
          e = lvRefElement(buffer, offset);
        } while (e == null);
      } else {
        return null;
      }
    }

    if (e == JUMP) {
      final E[] nextBuffer = nextBuffer(buffer, mask);
      return newBufferPoll(nextBuffer, index);
    }

    soRefElement(buffer, offset, null); // release element null
    soConsumerIndex(index + 2); // release cIndex
    return (E) e;
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is correct for single consumer thread use only.
   */
  @SuppressWarnings("unchecked")
  @Override
  public E peek() {
    final E[] buffer = consumerBuffer;
    final long index = lpConsumerIndex();
    final long mask = consumerMask;

    final long offset = modifiedCalcCircularRefElementOffset(index, mask);
    Object e = lvRefElement(buffer, offset);
    if (e == null && index != lvProducerIndex()) {
      // peek() == null iff queue is empty, null element is not strong enough indicator, so we must
      // check the producer index. If the queue is indeed not empty we spin until element is
      // visible.
      do {
        e = lvRefElement(buffer, offset);
      } while (e == null);
    }
    if (e == JUMP) {
      return newBufferPeek(nextBuffer(buffer, mask), index);
    }
    return (E) e;
  }

  /** We do not inline resize into this method because we do not resize on fill. */
  private int offerSlowPath(long mask, long pIndex, long producerLimit) {
    final long cIndex = lvConsumerIndex();
    long bufferCapacity = getCurrentBufferCapacity(mask);

    if (cIndex + bufferCapacity > pIndex) {
      if (!casProducerLimit(producerLimit, cIndex + bufferCapacity)) {
        // retry from top
        return RETRY;
      } else {
        // continue to pIndex CAS
        return CONTINUE_TO_P_INDEX_CAS;
      }
    }
    // full and cannot grow
    else if (availableInQueue(pIndex, cIndex) <= 0) {
      // offer should return false;
      return QUEUE_FULL;
    }
    // grab index for resize -> set lower bit
    else if (casProducerIndex(pIndex, pIndex + 1)) {
      // trigger a resize
      return QUEUE_RESIZE;
    } else {
      // failed resize attempt, retry from top
      return RETRY;
    }
  }

  /** @return available elements in queue * 2 */
  protected abstract long availableInQueue(long pIndex, long cIndex);

  @SuppressWarnings("unchecked")
  private E[] nextBuffer(final E[] buffer, final long mask) {
    final long offset = nextArrayOffset(mask);
    final E[] nextBuffer = (E[]) lvRefElement(buffer, offset);
    consumerBuffer = nextBuffer;
    consumerMask = (length(nextBuffer) - 2) << 1;
    soRefElement(buffer, offset, BUFFER_CONSUMED);
    return nextBuffer;
  }

  private static long nextArrayOffset(long mask) {
    return modifiedCalcCircularRefElementOffset(mask + 2, Long.MAX_VALUE);
  }

  private E newBufferPoll(E[] nextBuffer, long index) {
    final long offset = modifiedCalcCircularRefElementOffset(index, consumerMask);
    final E n = lvRefElement(nextBuffer, offset);
    if (n == null) {
      throw new IllegalStateException("new buffer must have at least one element");
    }
    soRefElement(nextBuffer, offset, null);
    soConsumerIndex(index + 2);
    return n;
  }

  private E newBufferPeek(E[] nextBuffer, long index) {
    final long offset = modifiedCalcCircularRefElementOffset(index, consumerMask);
    final E n = lvRefElement(nextBuffer, offset);
    if (null == n) {
      throw new IllegalStateException("new buffer must have at least one element");
    }
    return n;
  }

  @Override
  public long currentProducerIndex() {
    return lvProducerIndex() / 2;
  }

  @Override
  public long currentConsumerIndex() {
    return lvConsumerIndex() / 2;
  }

  @Override
  public abstract int capacity();

  @Override
  public boolean relaxedOffer(E e) {
    return offer(e);
  }

  @SuppressWarnings("unchecked")
  @Override
  public E relaxedPoll() {
    final E[] buffer = consumerBuffer;
    final long index = lpConsumerIndex();
    final long mask = consumerMask;

    final long offset = modifiedCalcCircularRefElementOffset(index, mask);
    Object e = lvRefElement(buffer, offset);
    if (e == null) {
      return null;
    }
    if (e == JUMP) {
      final E[] nextBuffer = nextBuffer(buffer, mask);
      return newBufferPoll(nextBuffer, index);
    }
    soRefElement(buffer, offset, null);
    soConsumerIndex(index + 2);
    return (E) e;
  }

  @SuppressWarnings("unchecked")
  @Override
  public E relaxedPeek() {
    final E[] buffer = consumerBuffer;
    final long index = lpConsumerIndex();
    final long mask = consumerMask;

    final long offset = modifiedCalcCircularRefElementOffset(index, mask);
    Object e = lvRefElement(buffer, offset);
    if (e == JUMP) {
      return newBufferPeek(nextBuffer(buffer, mask), index);
    }
    return (E) e;
  }

  @Override
  public int fill(Supplier<E> s) {
    long result =
        0; // result is a long because we want to have a safepoint check at regular intervals
    final int capacity = capacity();
    do {
      final int filled = fill(s, PortableJvmInfo.RECOMENDED_OFFER_BATCH);
      if (filled == 0) {
        return (int) result;
      }
      result += filled;
    } while (result <= capacity);
    return (int) result;
  }

  @Override
  public int fill(Supplier<E> s, int limit) {
    if (null == s) throw new IllegalArgumentException("supplier is null");
    if (limit < 0) throw new IllegalArgumentException("limit is negative:" + limit);
    if (limit == 0) return 0;

    long mask;
    E[] buffer;
    long pIndex;
    int claimedSlots;
    while (true) {
      long producerLimit = lvProducerLimit();
      pIndex = lvProducerIndex();
      // lower bit is indicative of resize, if we see it we spin until it's cleared
      if ((pIndex & 1) == 1) {
        continue;
      }
      // pIndex is even (lower bit is 0) -> actual index is (pIndex >> 1)

      // NOTE: mask/buffer may get changed by resizing -> only use for array access after successful
      // CAS.
      // Only by virtue offloading them between the lvProducerIndex and a successful
      // casProducerIndex are they
      // safe to use.
      mask = this.producerMask;
      buffer = this.producerBuffer;
      // a successful CAS ties the ordering, lv(pIndex) -> [mask/buffer] -> cas(pIndex)

      // we want 'limit' slots, but will settle for whatever is visible to 'producerLimit'
      long batchIndex =
          Math.min(producerLimit, pIndex + 2l * limit); //  -> producerLimit >= batchIndex

      if (pIndex >= producerLimit) {
        int result = offerSlowPath(mask, pIndex, producerLimit);
        switch (result) {
          case CONTINUE_TO_P_INDEX_CAS:
            // offer slow path verifies only one slot ahead, we cannot rely on indication here
          case RETRY:
            continue;
          case QUEUE_FULL:
            return 0;
          case QUEUE_RESIZE:
            resize(mask, buffer, pIndex, null, s);
            return 1;
        }
      }

      // claim limit slots at once
      if (casProducerIndex(pIndex, batchIndex)) {
        claimedSlots = (int) ((batchIndex - pIndex) / 2);
        break;
      }
    }

    for (int i = 0; i < claimedSlots; i++) {
      final long offset = modifiedCalcCircularRefElementOffset(pIndex + 2l * i, mask);
      soRefElement(buffer, offset, s.get());
    }
    return claimedSlots;
  }

  @Override
  public void fill(Supplier<E> s, WaitStrategy wait, ExitCondition exit) {
    MessagePassingQueueUtil.fill(this, s, wait, exit);
  }

  @Override
  public int drain(Consumer<E> c) {
    return drain(c, capacity());
  }

  @Override
  public int drain(Consumer<E> c, int limit) {
    return MessagePassingQueueUtil.drain(this, c, limit);
  }

  @Override
  public void drain(Consumer<E> c, WaitStrategy wait, ExitCondition exit) {
    MessagePassingQueueUtil.drain(this, c, wait, exit);
  }

  /**
   * Get an iterator for this queue. This method is thread safe.
   *
   * <p>The iterator provides a best-effort snapshot of the elements in the queue. The returned
   * iterator is not guaranteed to return elements in queue order, and races with the consumer
   * thread may cause gaps in the sequence of returned elements. Like {link #relaxedPoll}, the
   * iterator may not immediately return newly inserted elements.
   *
   * @return The iterator.
   */
  @Override
  public Iterator<E> iterator() {
    return new WeakIterator(consumerBuffer, lvConsumerIndex(), lvProducerIndex());
  }

  private static class WeakIterator<E> implements Iterator<E> {
    private final long pIndex;
    private long nextIndex;
    private E nextElement;
    private E[] currentBuffer;
    private int mask;

    WeakIterator(E[] currentBuffer, long cIndex, long pIndex) {
      this.pIndex = pIndex >> 1;
      this.nextIndex = cIndex >> 1;
      setBuffer(currentBuffer);
      nextElement = getNext();
    }

    @Override
    public void remove() {
      throw new UnsupportedOperationException("remove");
    }

    @Override
    public boolean hasNext() {
      return nextElement != null;
    }

    @Override
    public E next() {
      final E e = nextElement;
      if (e == null) {
        throw new NoSuchElementException();
      }
      nextElement = getNext();
      return e;
    }

    private void setBuffer(E[] buffer) {
      this.currentBuffer = buffer;
      this.mask = length(buffer) - 2;
    }

    private E getNext() {
      while (nextIndex < pIndex) {
        long index = nextIndex++;
        E e = lvRefElement(currentBuffer, calcCircularRefElementOffset(index, mask));
        // skip removed/not yet visible elements
        if (e == null) {
          continue;
        }

        // not null && not JUMP -> found next element
        if (e != JUMP) {
          return e;
        }

        // need to jump to the next buffer
        int nextBufferIndex = mask + 1;
        Object nextBuffer = lvRefElement(currentBuffer, calcRefElementOffset(nextBufferIndex));

        if (nextBuffer == BUFFER_CONSUMED || nextBuffer == null) {
          // Consumer may have passed us, or the next buffer is not visible yet: drop out early
          return null;
        }

        setBuffer((E[]) nextBuffer);
        // now with the new array retry the load, it can't be a JUMP, but we need to repeat same
        // index
        e = lvRefElement(currentBuffer, calcCircularRefElementOffset(index, mask));
        // skip removed/not yet visible elements
        if (e == null) {
          continue;
        } else {
          return e;
        }
      }
      return null;
    }
  }

  private void resize(long oldMask, E[] oldBuffer, long pIndex, E e, Supplier<E> s) {
    assert (e != null && s == null) || (e == null || s != null);
    int newBufferLength = getNextBufferSize(oldBuffer);
    final E[] newBuffer;
    try {
      newBuffer = allocateRefArray(newBufferLength);
    } catch (OutOfMemoryError oom) {
      assert lvProducerIndex() == pIndex + 1;
      soProducerIndex(pIndex);
      throw oom;
    }

    producerBuffer = newBuffer;
    final int newMask = (newBufferLength - 2) << 1;
    producerMask = newMask;

    final long offsetInOld = modifiedCalcCircularRefElementOffset(pIndex, oldMask);
    final long offsetInNew = modifiedCalcCircularRefElementOffset(pIndex, newMask);

    soRefElement(newBuffer, offsetInNew, e == null ? s.get() : e); // element in new array
    soRefElement(oldBuffer, nextArrayOffset(oldMask), newBuffer); // buffer linked

    // ASSERT code
    final long cIndex = lvConsumerIndex();
    final long availableInQueue = availableInQueue(pIndex, cIndex);
    RangeUtil.checkPositive(availableInQueue, "availableInQueue");

    // Invalidate racing CASs
    // We never set the limit beyond the bounds of a buffer
    soProducerLimit(pIndex + Math.min(newMask, availableInQueue));

    // make resize visible to the other producers
    soProducerIndex(pIndex + 2);

    // INDEX visible before ELEMENT, consistent with consumer expectation

    // make resize visible to consumer
    soRefElement(oldBuffer, offsetInOld, JUMP);
  }

  /** @return next buffer size(inclusive of next array pointer) */
  protected abstract int getNextBufferSize(E[] buffer);

  /** @return current buffer capacity for elements (excluding next pointer and jump entry) * 2 */
  protected abstract long getCurrentBufferCapacity(long mask);
}
